1. Field of the Invention
The present invention relates to a drive control system for an electric vehicle and a method of drive control of an electric vehicle.
2. Description of the Related Art
In the related art, a vehicle drive system mounted to a hybrid vehicle as an electric vehicle and adapted to transmit part of engine torque, which is a torque of an engine, to a generator (a generator motor), and transmit the rest of the engine torque to driving wheels, includes a planetary gear unit having a sun gear, a ring gear, and a carrier, and is configured in such a manner that the carrier and the engine are connected, the ring gear and the drive motor are connected to the driving wheels, and the sun gear and the generator are connected so that rotation outputted from the ring gear and the drive motor is transmitted to the driving wheels to generate drive power.
Then, in the vehicle drive system, an inverter is disposed between the drive motor and a drive motor control unit, the inverter is driven based on a drive signal fed from the drive motor control unit, receives a DC current from a battery, generates U-phase, V-phase, and W-phase currents, and supplies the currents of the respective phases to the drive motor. In order to do so, the inverter includes a plurality of transistors, for example, six transistors, as switching elements, and the transistors, being unitized by pairs, constitute transistor modules, Insulated Gate Bipolar Transistor, (IGBT) in the respective phases. Therefore, when the drive signal is sent to the respective transistors in a predetermined pattern, the transistors are turned ON and OFF and generate currents in the respective phases.
Then, a rotor position which represents a position of a rotor of the drive motor is detected, the drive motor revolution number, which is a revolution number of the drive motor, is calculated based on the rotor position, and control of a drive motor torque, which is a torque of the drive motor for example, is performed based on the drive motor revolution number.
The hybrid vehicle having a structure as described above is adapted in such a manner that a forward travel range, a reverse travel range, a neutral range, and a parking range can be selected by operating a shift lever. When the parking range is selected, the driving wheels are locked, and the hybrid vehicle is maintained in a stopped state (for example, see JP-A-5-278483).
Therefore, the ring gear is integrally formed with a parking gear, so that when a driver operates the shift lever and selects the parking range, a parking mechanism is activated, a swingably disposed clawed pole is brought into engagement with the parking gear to lock the parking gear, whereby the driving wheels are locked.
However, in the hybrid vehicle in the related art, for example, when the engine torque varies because the engine is started or stopped in a state in which the parking mechanism is activated, an abnormal grating sound may be generated between the clawed pole and the parking gear in the parking mechanism.
In other words, when starting the engine in the hybrid vehicle, it is necessary to obtain an engine revolution number, which is a revolution number of the engine, of a value suitable for starting the engine. Therefore, the generator is activated and increases a generator revolution number, which is a revolution number of the generator. At this time, it is necessary to cause a predetermined drive motor torque to be generated by the drive motor corresponding to a generator torque, which is a torque of the generator in order to receive a reaction force generated when rotating the engine. However, when noise is added to a sensor output from a position sensor that detects the rotor position upon driving the drive motor, the drive motor torque cannot be generated with high degree of accuracy, and consequently, the grating sound may occur between claws of the clawed pole and teeth of the parking gear due to backlash.
On the other hand, when stopping the engine of the hybrid vehicle, it is necessary to obtain the engine revolution number of a value suitable for stopping the engine. Therefore, the generator revolution number is reduced to a negative value. At this time, it is necessary to reduce the drive motor torque in association with the decrease in the generator torque. In this case as well, the grating sound may occur.